/*

 * Copyright © 2015 Canonical Limited

 *

 * SPDX-License-Identifier: LGPL-2.1-or-later

 *

 * This library is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * This library is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with this library; if not, see <http://www.gnu.org/licenses/>.

 *

 * Author: Ryan Lortie <desrt@desrt.ca>

 */

#include "config.h"

#include "gcontextspecificgroup.h"

#include <glib-object.h>

#include "glib-private.h"

typedef struct

{

  GSource   source;

  GMutex    lock;

  gpointer  instance;

  GQueue    pending;

} GContextSpecificSource;

static gboolean

g_context_specific_source_dispatch (GSource     *source,

                                    GSourceFunc  callback,

                                    gpointer     user_data)

{

  GContextSpecificSource *css = (GContextSpecificSource *) source;

  guint signal_id;

  g_mutex_lock (&css->lock);

  g_assert (!g_queue_is_empty (&css->pending));

  signal_id = GPOINTER_TO_UINT (g_queue_pop_head (&css->pending));

  if (g_queue_is_empty (&css->pending))

    g_source_set_ready_time (source, -1);

  g_mutex_unlock (&css->lock);

  g_signal_emit (css->instance, signal_id, 0);

  return TRUE;

}

static void

g_context_specific_source_finalize (GSource *source)

{

  GContextSpecificSource *css = (GContextSpecificSource *) source;

  g_mutex_clear (&css->lock);

  g_queue_clear (&css->pending);

}

static GContextSpecificSource *

g_context_specific_source_new (const gchar *name,

                               gpointer     instance)

{

  static GSourceFuncs source_funcs = {

    NULL,

    NULL,

    g_context_specific_source_dispatch,

    g_context_specific_source_finalize,

    NULL, NULL

  };

  GContextSpecificSource *css;

  GSource *source;

  source = g_source_new (&source_funcs, sizeof (GContextSpecificSource));

  css = (GContextSpecificSource *) source;

  g_source_set_name (source, name);

  g_mutex_init (&css->lock);

  g_queue_init (&css->pending);

  css->instance = instance;

  return css;

}

static gboolean

g_context_specific_group_change_state (gpointer user_data)

{

  GContextSpecificGroup *group = user_data;

  g_mutex_lock (&group->lock);

  if (group->requested_state != group->effective_state)

    {

      (* group->requested_func) ();

      group->effective_state = group->requested_state;

      group->requested_func = NULL;

      g_cond_broadcast (&group->cond);

    }

  g_mutex_unlock (&group->lock);

  return FALSE;

}

/* this is not the most elegant way to deal with this, but it's probably

 * the best.  there are only two other things we could do, really:

 *

 *  - run the start function (but not the stop function) from the user's

 *    thread under some sort of lock.  we don't run the stop function

 *    from the user's thread to avoid the destroy-while-emitting problem

 *

 *  - have some check-and-compare functionality similar to what

 *    gsettings does where we send an artificial event in case we notice

 *    a change during the potential race period (using stat, for

 *    example)

 */

static void

g_context_specific_group_request_state (GContextSpecificGroup *group,

                                        gboolean               requested_state,

                                        GCallback              requested_func)

{

  if (requested_state != group->requested_state)

    {

      if (group->effective_state != group->requested_state)

        {

          /* abort the currently pending state transition */

          g_assert (group->effective_state == requested_state);

          group->requested_state = requested_state;

          group->requested_func = NULL;

        }

      else

        {

          /* start a new state transition */

          group->requested_state = requested_state;

          group->requested_func = requested_func;

          g_main_context_invoke (GLIB_PRIVATE_CALL(g_get_worker_context) (),

                                 g_context_specific_group_change_state, group);

        }

    }

  /* we only block for positive transitions */

  if (requested_state)

    {

      while (group->requested_state != group->effective_state)

        g_cond_wait (&group->cond, &group->lock);

      /* there is no way this could go back to FALSE because the object

       * that we just created in this thread would have to have been

       * destroyed again (from this thread) before that could happen.

       */

      g_assert (group->effective_state);

    }

}

gpointer

g_context_specific_group_get (GContextSpecificGroup *group,

                              GType                  type,

                              goffset                context_offset,

                              GCallback              start_func)

{

  GContextSpecificSource *css;

  GMainContext *context;

  context = g_main_context_get_thread_default ();

  if (!context)

    context = g_main_context_default ();

  g_mutex_lock (&group->lock);

  if (!group->table)

    group->table = g_hash_table_new (NULL, NULL);

  css = g_hash_table_lookup (group->table, context);

  if (!css)

    {

      gpointer instance;

      instance = g_object_new (type, NULL);

      css = g_context_specific_source_new (g_type_name (type), instance);

      G_STRUCT_MEMBER (GMainContext *, instance, context_offset) = g_main_context_ref (context);

      g_source_attach ((GSource *) css, context);

      g_hash_table_insert (group->table, context, css);

    }

  else

    g_object_ref (css->instance);

  if (start_func)

    g_context_specific_group_request_state (group, TRUE, start_func);

  g_mutex_unlock (&group->lock);

  return css->instance;

}

void

g_context_specific_group_remove (GContextSpecificGroup *group,

                                 GMainContext          *context,

                                 gpointer               instance,

                                 GCallback              stop_func)

{

  GContextSpecificSource *css;

  if (!context)

    {

      g_critical ("Removing %s with NULL context.  This object was probably directly constructed from a "

                  "dynamic language.  This is not a valid use of the API.", G_OBJECT_TYPE_NAME (instance));

      return;

    }

  g_mutex_lock (&group->lock);

  css = g_hash_table_lookup (group->table, context);

  g_hash_table_remove (group->table, context);

  g_assert (css);

  /* stop only if we were the last one */

  if (stop_func && g_hash_table_size (group->table) == 0)

    g_context_specific_group_request_state (group, FALSE, stop_func);

  g_mutex_unlock (&group->lock);

  g_assert (css->instance == instance);

  g_source_destroy ((GSource *) css);

  g_source_unref ((GSource *) css);

  g_main_context_unref (context);

}

void

g_context_specific_group_emit (GContextSpecificGroup *group,

                               guint                  signal_id)

{

  g_mutex_lock (&group->lock);

  if (group->table)

    {

      GHashTableIter iter;

      gpointer value;

      gpointer ptr;

      ptr = GUINT_TO_POINTER (signal_id);

      g_hash_table_iter_init (&iter, group->table);

      while (g_hash_table_iter_next (&iter, NULL, &value))

        {

          GContextSpecificSource *css = value;

          g_mutex_lock (&css->lock);

          g_queue_remove (&css->pending, ptr);

          g_queue_push_tail (&css->pending, ptr);

          g_source_set_ready_time ((GSource *) css, 0);

          g_mutex_unlock (&css->lock);

        }

    }

  g_mutex_unlock (&group->lock);

}